Marriage and later life
In 1824, Harriet and the rest of the family moved to Brussels upon the appointment of Leveson-Gower, now Viscount Granville, as British ambassador to The Hague. Talks of finding a husband for Harriet began, and she was given lessons on etiquette from a dancing master. Viscountess Granville worried that her charge's marriage prospects would face difficulties, namely due to her mysterious status as a ward and lack of a dowry. The girl had many positive qualities, however; the historian Janet Gleeson describes Harriet as "well-mannered and physically attractive to the opposite sex."
While in the Netherlands, Harriet met Hon. George Osborne, the son of Francis Osborne, 1st Baron Godolphin and first cousin to the 7th Duke of Leeds who had no issue, thus he became the heir to the dukedom of Leeds. Granville and Baron Godolphin eventually gave their consent, and the couple were married at the British Embassy in Paris on 21 October 1824. The newly married couple took up residence in the Bois de Boulogne, where they were enthusiastically welcomed by French society.
Osborne and Harriet faced constant financial problems, living far beyond their means to the point of almost being jailed. Harriet and her brother, George Arundel Stewart, were both hopeless with money. This is a trait they inherited from their mother. Although George Arundel Stewart debt was far less than Harriet’s debt, George Arundel Stewart's debt was at times about £800. In times like this, Harriet would turn to her brother for help, and George Arundel Stewart would report this matter to their father, who would step in to help Harriet out. Her father and guardian, now 1st Earl Granville, could usually be depended on to help with their debts, to Harriet's embarrassment. In one letter, she wrote to him, "I can never be sufficiently grateful to you for the kindness you have again shown me and for the generosity with which you have again relieved our great difficulties. I feel much shame at our having brought these difficulties upon ourselves again."
George Arundel Stewart's life remains more mysterious. George Arundel Stewart travelled a lot and would bring gifts, Indian turbans, shawls, fans, and a chess set, from Asia and India. George Arundel Stewart was personable and sociable. Yet, he never married, and his half-siblings adore him. When the family was about to disembark from Ramsgate, George Arundel Stewart would wrap his coat to around his siblings and carry his siblings along the pier to the inn. George Arundel Stewart became his father’s private secretary. They were fond of each other and travel together for six months in Spain in 1847. George Arundel Stewart died in 1875.
Osborne inherited his father's title of Baron Godolphin in 1850, making Harriet Baroness Godolphin, known as "Lady Godolphin". She died at the family home in Stapleford, Cambridgeshire, on 28 October 1852, seven years before Osborne succeeded his first cousin as the 8th Duke of Leeds, had she lived longer, Harriet would have been titled "Her grace, the Duchess of Leeds".
Osborne did not marry again and died on 8 August 1872, after which their eldest surviving son George Godolphin succeeded to the dukedom. A hatchment of the Duke's arms on his death survives; unusually, for a Duke, his wife is shown as having no right to inherit her own coat of arms (because of her illegitimate birth) and yet this is not glossed over by omitting the place for her arms on the hatchment. Instead, the hatchment shows decorative swirls on the wife's side (the right-hand side) of the shield of arms where her own paternal arms would otherwise have been.
